If BVB receive a rival bid from Manchester United, however, the English side would have to be preferred over the Bavarians. Lewandowski has been linked to the Premier League champions since last December, and the The Daily Mail this week claim they are ready to increase their bid to £30 million.

If Wayne Rooney departs—or is moved to a permanent attacking midfield role—there would be room for Lewandowski in the attacking line. Yet the Pole plays the "traditional No. 9" position that has been moulded around Robin van Persie, so some adjustment would surely be needed.

Radamel Falcao

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With 62 La Liga goals across two seasons with Atletico Madrid, Radamel Falcao has become a top transfer priority for many of Europe's major clubs.

The double Europa League winner—and double Europa League top scorer—has been linked with a move to Chelsea since last season, but reportedly declined a January window transfer move out of loyalty to Atleti.

This week, the British press believe the Blues will be bringing in assets from both sides of Madrid: Roman Abramovich will buy Falcao as a gift for returning coach Jose Mourinho, say The Mirror (among others).Yet there is also plenty of speculation around the Colombian arriving at the Theatre of Dreams. The Daily Mail believe a cash-plus-player deal with Javier Hernandez is on the cards, with the £20 million-rated Chicharito being supplemented by £27 million cold hard cash.

Like Lewandowski, Falcao is a powerful No. 9 whose role might conflict with the role Robin van Persie has played at United this season. B/R's Will Tidey, however, makes the case for them playing together, along with Rooney.

Asmir Begovic

Despite keeping 11 2012-13 Premier League clean sheets and pulling off a formidable performance in the Champions League, rumours persist that Sir Alex finds David de Gea too prone to mistakes.

Sources such as The Metro believe Iker Casillas is being lined up to replace the young Spaniard. But when his adversary Jose Mourinho inevitably leaves the Bernabeu this summer, it seems likely that the Patron Saint of Real Madrid's defence will stay put.

A more likely goalkeeper transfer target is Asmir Begovic, who was part of the Stoke defence that looked very impressive in the first half of the season, but has lost all sense of cohesiveness in recent matches.

In January, The Daily Mail claimed Begovic had his "heart set on" a £15 million move to Old Trafford, having received interest from the likes of Arsenal and Liverpool, too.

The Potters shot-stopper may lack the "big match" experience of someone like Casillas—and replacing a 22-year-old keeper with a 25-year-old one isn't really a move made out of a desire for more experience—but Begovic has already proven himself against the Premier League's best strikers.

Cristiano Ronaldo

The Portuguese star is under contract until 2015, but has stalled on renegotiating. Could he return to the club he loves, and the manager for whom he has unwavering respect?

According to The Mirror, the move is a distinct possibility thanks to his sponsor, Nike. Manchester United's kit manufacturer are said to be interested in renewing their £320 million sponsorship deal, and are keen to help him move away from his current Adidas-wearing employees.

American sponsors Chevrolet are also said to be willing to help fund a £55 million bid and his rumored £250,000 weekly wages.Furthermore, United legend Gary Pallister told Goal.com that Sir Alex is equally as keen as the sponsors to bring Ronaldo back to the Premier League.

At 28 years old, Ronaldo still has several peak seasons left in him, and very few other players in world football can guarantee goals like he can.

If there's one person worth emptying the war chest for this summer, it's C-Ron.

The precocious Hoops star has already rejected an offer of an extension to his four-year contract at Parkhead, leading many to believe he will leave Scotland. In the January window, The Express and Sky Sports both linked Wanyama with a move to Old Trafford.

The defensive midfielder—who has netted six SPL goals this term—would appear a good fit within Manchester United's squad, with plenty of physicality and defensive nous. As B/R's Max Towle points out, he would line up well alongside Michael Carrick or Tom Cleverley, but less so in central midfield.

This week, Wanyama said he will play with Celtic next season (via the BBC), but it would be very hard to turn down an offer from the reigning Premiership champions.